An AFM study of the topography of natural MoS2 following treatment in an RF-oxygen plasma

The results obtained in the study of the morphological modification of a natural molybdenum disulphide (MoS2) surface during radio frequency (RF)-oxygen plasma treatment are presented. The surface features observed following etching in oxygen plasmas show a strong dependence on the plasma power and the corresponding gas pressure. At low powers chemical modification was found to lead to semi-regular surface disruption at nano-scales, behaviour attributed to basal plane contraction of the material resulting from the substitution in the surface layers of sulphur by oxygen during etching. This chemical effect may be promoted by the simultaneous physical bombardment of the surface by the relatively energetic particles present in the plasma. However, increasing the plasma power appears to reduce the lateral layer-plane disruption and, instead, leads to a more random, less-structured sputtering of the surface material. This latter process, depending on the particular plasma conditions used, leaves irregular-sized disrupted features as humps or flakes in the observed topography. (C) 1999 Elsevier Science B.V. All rights reserved.